The invention relates to a signalling method in a wireless digital telecommunication system between a base station and a terminal, where the signals between the base station and the terminal are generated from bursts comprising symbols, each of the symbols being generated from several bits by modulating, the symbols comprising at least one stealing symbol indicating, if necessary, the use of a traffic channel for signalling.
The invention further relates to a wireless digital telecommunication system for signalling between a base station and a terminal, where the signals to be transmitted over a radio connection between the base station and the terminal comprise bursts generated from symbols, each of the symbols being generated from several bits by modulating, the symbols comprising at least one stealing symbol indicating, if necessary, the use of a traffic channel for signalling, the system comprising at least one transmitter and at least one receiver, whereof the transmitter comprises means that include a transmitting signalling message and the receiver includes means for identifying the signalling message.
In digital radio systems, call-related signalling between a base station and a terminal occurs simultaneously with a call to be transferred on a traffic channel. The GSM system, for example, employs two signalling channels for conducting call-related signalling, a SACCH (Slow Associated Control Channel) and a FACCH (Fast Associated Control Channel). The SACCH is a separate low-rate signalling channel associated with each traffic channel. Due to its low rate the channel can be used for non-urgent signalling only. The FACCH is fast signalling within the traffic channel, and can be used for time-critical signalling. However, a part of the traffic channel capacity is then lost.
In digital radio systems, such as the GSM system, data transmission occurs in bursts, and a specific burst structure is determined for each purpose, like data and signalling transmission, synchronization or equalization. A normal burst used for data and signalling transmission comprises a training sequence in the middle which includes a set of predetermined symbols that the receiver identifies. When comparing the received training sequence with a known training sequence the receiver may create information of the distortion caused by an un-ideal radio path to the received signal. On the basis of this information the receiver can demodulate the received signal more efficiently. The applicant""s previous patent application PCT/FI97/00465 describes a signalling method, in which a training sequence is used for signalling, that speeds up the signalling and leaves the entire traffic channel to be used by the payload.
The problem with the above system is the number of different training sequences required for transmitting versatile signals. One training sequence may describe one signalling message only and if the aim is to perform, for example, power control signalling including eight steps, eight different training sequences are required. If several signalling events are to be performed using the above method, the number of training sequences easily increases significantly. This increases the receiver load and complicates the implementation of the receiver, as the received training sequence must be separately compared with each known training sequence. Distinguishing training sequences from one another in particular becomes more difficult when the reception conditions are poor. Furthermore, when higher data transmission rates are aimed at, the use of a training sequence no longer guarantees fast enough signalling owing to the above and since the duration of the training sequence is relatively long bearing in mind that the training sequence is capable of transmitting one message only. Due to these drawbacks said method has not been widely employed and the GSM system, for example, still uses signalling channels.
It is thus an object of the invention to provide a method and an apparatus implementing the method so as to solve the above problems. The objects of the invention are achieved with a method, characterized by
using said stealing symbol for transmitting different signalling messages.
The wireless digital telecommunication system of the invention is characterized in that
the transmitter comprises means for coding different signalling messages, means for connecting the coded signalling message with the stealing symbols of the signal to be transmitted and means for modulating the signal so that each symbol comprises several bits and in that
the receiver comprises means for demodulating the received signal comprising symbols, means for generating the coded signalling message from the stealing symbols in the received signal and means for decoding the coded signalling message.
According to a preferred embodiment of the invention a code word corresponding to a signalling message to be transferred is formed using stealing symbols. The code word is placed into one or more stealing symbols. According to another preferred embodiment of the invention said code word is interleaved into the stealing symbols of several bursts. According to a further preferred embodiment of the invention the method is used for adjusting the transmission power of the mobile station and the base station.
The invention is based on the idea that the stealing symbols in a burst structure are used for transmitting signalling information. Stealing symbols have typically been used in a normal burst to indicate whether the data bits in a burst are allocated to be used on a traffic channel or stolen to be used on the FACCH. When planning systems that use higher data transmission rates, a way to increase the data transmission rate is to use such modulation methods where several bits are modulated into a transferable symbol. Then, the data transmission capacity of one symbol increases, and the symbol can be used for transmitting more information.
An advantage with the method and system of the invention is the signalling rate that is approximately 25 times faster than the SACCH signalling. As the data transmission rates increase, the signalling rates must also be increased. Another advantage with the invention is that the data transmission capacity of the traffic channel is not used for the signalling according to the invention. The method of the invention utilizes the signalling capacity that would otherwise be unused. The invention also creates for the different logical traffic channel types a new common signalling procedure from the base station to the mobile station and vice versa that has not previously been available, for example, with power control or link adaptation. A further advantage of the invention is that the signalling load does not increase when utilizing the invention.